Effects Of Light Cycles On Production Performance And Circadian Rhythm Of Laying Hens

Light is an important environmental factor that affects the reproductive development and production performance of laying hens.Firstly,we investigate the effects of light cycles on the development in growing period and the following reproduction in laying period of laying hens,by modulating the light cycles of growing hens;Secondly,we further investigate the effects of light cycles on the neuroendocrine,circadian rhythm and laying performance,by modulating the light cycles of late-laying hens;Finally,we investigate the effects of melatonin on the circadian rhythm and laying performance by treating late-laying hens with exogenous melatonin.This study provides theoretical data for lighting parameters of laying hens,and explains the regulatory mechanism of light on reproductive activities of laying hens.Experiment 1.Effect of different light reducing methods during growing period on growth,development and reproduction of laying hens.Two hundred and sixteen 9-week-old ISA Brown laying hens were randomly divided into 3 groups: the light time reduced 1 h per week until to 8 h finally(D1),light time reduced 2 h per week until 8 h finally(D2);and light time reduced from 14 h to 8 h directly(C8).The experiment was conducted for 8 weeks,10 hens were randomly selected from each group,and body weights were recorded,and liver,abdominal fat,oviduct and ovary were collected.At the age of 22 weeks,they are transferred to the laying house,and the production performance was counted weekly.The results showed that different light reduction methods had no significant effect on the growth and development of ovary and oviduct in laying hens(P>0.05).The feed intake increased significantly in D1group(P<0.05).The weight gain of the laying hens increased rapidly in the early test period(11~14 W)than the late period(15~18 W).During the egg-laying period,the egg laying rate was higher in the group of D1 at 24~29 W,at 34~43 W,however,the egg production rate was higher in the C8 group.Before 39 W,the average egg weight was greater in the group of D1.After 39 W,the average egg weight was higher in the C8 and D1 than in the D2.It was shown that the declining light with 1 h every week in the growing period accelerated the peak period of laying hens.The constant 8 h light during the growing period delays the time when layinghens enter the peak of egg production,but it also prolongs the duration of the peak period of egg production and saves energy.Experiment 2.Effects of different light cycles during late-laying period on production performance and circadian rhythm of laying hens.One hundred and ninety two 78-week-old Hyland Brown hens were randomly divided into 4 groups: 16L:8D control group,13L:15D photoperiod group(1 week contains 6 cycles),8L:5D:6L:5D intermittent light group,14L:5D:1L:4D intermittent light group.The egg production rate and egg weight were counted daily,and the feed intake was measured weekly.After 8 weeks of experiment,the blood samples,hypothalamus,pituitary,liver,ovary and eggshell gland were collected.As the results shown,compared with the 16L:8D group,the egg production rate in the 13L:15D group decreased significantly(P<0.05),and the average egg weight increased significantly(P<0.05),and the contents of GnRH and GnIH in blood increased,while the contents of LH and FSH in blood decreased.By comparing the mRNA levels of the two groups,the mRNA expressions of FSHR and LHR are in a cooperative manner.There is a feedback mechanism of the clock in the hypothalamus,pituitary,ovarian and eggshell glands of the hens.Photoperiod can change the endogenous circadian rhythm of the peripheral clock,thereby effecting laying rate.Experiment 3.Effects of exogenous melatonin on the performance of late-laying hens.Seventy two 78-week-old Hyland Brown hens were randomly divided into 2 groups,and were treated with either 0 or 10 mg of melatonin implants under the neck skin of the birds.The experiment was carried out for 8 weeks.The egg production rate and egg weight were counted daily,and the feed intake was measured weekly.At 4 weeks of the experiment,the quality of eggs was measured.At the 2,4 and 6 weeks of the experiment,8 birds of each group were taken blood at 12:00 AM and 0:00 PM respectively,to measure melatonin concentration in serum.The results showed that exogenous melatonin treatment had no significant effect on the production performance and egg quality of laying hens(P>0.05).The concentration of melatonin in the serum was lower at 12:00 AM than at 0:00 PM,and the concentration of melatonin in the blood was significantly increased after 4 weeks of exogenous melatonin treatment.However,there is no change in production performance.Theresults showed that melatonin implant cannot regulate endocrine regulation,biological rhythm and production performance of laying hens.